I heard a knock on the door. I opened it, and was surprised that he was a stranger. He said that he was Henry, my father's friend, and had lost his wallet and so had no money for lunch. He looked sad, so I gave him $10. He thanked me and left. When my father returned home, I told him my good deed in helping his friend. Instead of praising me, my father scolded me and said he did not have a friend whose name was Henry.
From this experience, I learn / learned / have learned never to trust strangers.
Which verb should I use?